The present invention was developed in connection with a sunshade umbrella such as one would use by a pool. The invention will be discussed in that context. However it is to be understood that the novel joint mechanism disclosed will find application outside that field, for example in the field of prosthetics.
Angularly adjustable, releasably lockable ball joints are commonly used as part of an umbrella assembly, to hold a suspended canopy locked at an angle to horizontal. Assemblies of this type are shown in U.S. Pat. Nos. 4,674,523, issued to Glatz, and No. 5,002,081, issued to Stromeyer. In general, these prior art ball joints involve:
a ball attached to a shank forming part of the suspension stand; PA1 an actuator or screw spindle carrying the canopy; PA1 a housing engaging the ball and spindle so that they cannot separate, but which is operative to enable the spindle to be angularly adjusted when the actuator is disengaged; and PA1 a concave socket or pin at the end of the spindle, for frictionally engaging the ball to lock the spindle and ball together and fix the canopy at a desired angle. PA1 U.S. Pat. Nos. 3,841,769 (Bowerman) and 4,620,813 (Lacher) show a socket having protuberances and a ball having dimples or indentations which engage to fix the orientation of the arms attached thereto; PA1 U.S. Pat. No. 3,691,788 (Mazziotti) shows a ball having a grooved surface and an actuator having a spherical tip which locks up by engaging a groove; PA1 U.S. Pat. No. 5,280,871 (Ching-Pao et al) and U.S. Pat. No. 3,433,510 (Hulterstrum) show a dimpled ball and an actuator having a spherical tip; and PA1 U.S. Pat. No. 892,105 (White) shows a ball and socket whose surfaces are both knurled. PA1 a rounded member having a plurality of concavities on its surface and being secured to the first part; PA1 a disengageable actuator having a rounded tip operative to be advanced, to lock up with the rounded member by penetrating a concavity, or to be retracted, to disengage them, said actuator being connected with the second part; and PA1 means for holding the parts, rounded member and actuator together while permitting the parts to change relative orientation when the actuator tip is retracted. PA1 the rounded member has a plurality of patterns of spaced-apart protuberances covering at least part of its surface, the protuberances of each pattern forming a concavity; PA1 the patterns and protuberances are consistent in shape, area and size and the patterns have regular polygonal configurations, preferably triangular or square; and PA1 the protuberances, actuator tip and pattern are dimensioned so that the tip may penetrate the concavity of the pattern and simultaneously contacts all of the protuberances of the pattern that it penetrates, but remains spaced from the surface of the rounded member at full penetration. PA1 the locking capability is greater than one obtains with a dimpled ball; PA1 by arranging the patterns in accordance with a geometric design, the longitude and latitude of the concavity sites is predictable; and PA1 the use of the triangular pattern yields a large number of concavity sites in the case of a rounded member that is spherical and of given diameter. Compared to an equivalent pattern of dimples, twice as many concavity sites result simply through the formation of the protuberances.
However, in windy conditions the frictional engagement of ball and socket has been found to be insufficient to hold the umbrella canopy angularly cocked. The socket can slip on the ball surface due to the high torsional forces experienced.
The work underlying the present invention was originally undertaken to provide a more reliable "lock-up" between the ball and the actuator comprising the screw spindle and concave socket.
At this point, it is appropriate to consider relevant prior art outside the suspension umbrella field. It is known in the context of angularly adjustable, releasably lockable ball joint assemblies to modify one or both of the engaging lock-up surfaces to create a better interlock. For example:
Applicant has tested a dimpled ball and spherical pin actuator, but has found the "lock-up" to be inadequate for use on suspension umbrellas.
The objective of the invention is therefore to modify a conventional joint mechanism such as a ball joint to provide a stronger locking action between the actuator and the spherical member.